This disclosure relates to computer-generated imagery (CGI) and computer-aided animation. More specifically, this disclosure relates to techniques for creating and editing hierarchical subdivision surface geometry for use in CGI and computer-aided animation.
With the wide-spread availability of computers, computer graphics artists and animators can rely upon computers to assist in production process for creating animations and computer-generated imagery (CGI). This may include using computers to have physical models be represented by virtual models in computer memory. Typically, two-dimensional (2D) or three-dimensional (3D) computer-aided animation combines 2D/3D models of objects and programmed movement of one or more of the models. In 3D computer animation, the first step is typically the object modeling process. Objects can be sculpted much like real clay or plaster, working from general forms to specific details, for example, with various sculpting tools. Models may then be constructed, for example, out of geometrical vertices, faces, and edges in a 3D coordinate system to represent the objects. These virtual models can then be manipulated using computers to, for example, simulate physics, design aesthetic actions such as poses or other deformations, crate lighting, coloring and paint, or the like, of characters or other elements of a computer animation display.
Pixar is one of the pioneering companies in the computer-generated imagery (CGI) and computer-aided animation industry. Pixar is more widely known as Pixar Animation Studios, the creators of animated features such as “Toy Story” (1995) and “Toy Story 2” (1999), “A Bugs Life” (1998), “Monsters, Inc.” (2001), “Finding Nemo” (2003), “The Incredibles” (2004), “Cars” (2006), “Ratatouille” (2007), and others. In addition to creating animated features, Pixar develops computing platforms and tools specially designed for computer-aided animation and CGI. One such example is now known as PhotoRealistic RenderMan, or PRMan for short. PRMan is a photorealistic RenderMan-compliant rendering software system based on the RenderMan Interface Specification (RISpec) which is Pixar's technical specification for a standard communications protocol (or interface) between 3D computer graphics programs and rendering programs. PRMan is produced by Pixar and used to render their in-house 3D animated movie productions. It is also available as a commercial product licensed to third parties, sold as part of a bundle called RenderMan Pro Server, a RenderMan-compliant rendering software system developed by Pixar based on their own interface specification. Other examples include tools and plug-ins for programs such as the AUTODESK MAYA high-end 3D computer graphics software package from AutoDesk, Inc. of San Rafael, Calif.
One core functional aspect of PRMan can include the use of a “rendering engine” to convert geometric and/or mathematical descriptions of objects into images. This process is known in the industry as “rendering.” For movies, other animated features, shorts, and special effects, a user (e.g., a skilled computer graphics artist) can specify the geometric or mathematical description of objects to be used in the rendered image or animation sequence, such as characters, props, background, or the like. In some instances, the geometric description of the objects may include a number of animation control variables (avars) and values for the avars. An animator may also pose the objects within the image or sequence and specify motions and positions of the objects over time to create an animation.
As such, the production of CGI and computer-aided animation may involve the extensive use of various computer graphics techniques to produce a visually appealing image from the geometric description of an object that may be used to convey an essential element of a story or provide a desired special effect. One of the challenges in creating these visually appealing images can be the balancing of a desire for a highly-detailed image of a character or other object with the practical issues involved in allocating the resources (both human and computational) required to produce those visually appealing images.
Interactive editing is of great importance for creating geometric models for a variety of applications, ranging from mechanical design to movie character creation. Often times, modeling begins with an existing object on which the user performs a sequence of editing operations that lead to a desired shape. Subdivision surfaces are a known modeling tool used in computer graphics that allow a user to begin, for example, with a polygonal base mesh and continuously divide the base mesh according to subdivision rules until continuous “smooth” surface results. Thus, subdivision surfaces define smooth curves or surfaces as the limit of a sequence of successive refinements that provide finer details to the mesh without having to add more geometry. Subdivision surfaces are increasing in popularity as a modeling tool, in part because these surfaces combine the benefits of both polygonal and NURBS modeling. Subdivision surfaces allow users to model smooth surfaces by manipulating a small set of control vertices.
Accordingly, what is desired is to solve one or more of the problems relating to creating and editing hierarchical subdivision surface geometry for use in CGI and computer-aided animation, some of which may be discussed herein. Additionally, what is desired is to reduce some of the drawbacks relating to creating and editing hierarchical subdivision surface geometry for use in CGI and computer-aided animation, some of which may be discussed herein.